[Stoves] Request to get partners in a possible TLUD stove improvement project

kgharris kgharris at sonic.net
Wed Aug 5 01:59:02 CDT 2015


All,

These are good discussions on burning CO and swirl.  I know that Aprovecho has developed a good charcoal stove based on experimentation by labratory manager Sam Bentson.  My own experience is much less but I do see in my TLUD combustor blue CO flames in the Venturi gas mixer after the hydrocarbon flames have gone out.  I do not know how thurough this burning of CO is.  My speculation is that thoroughly mixing adiquate air with the CO, and keeping a flame going above the coals, as per Sam's findings, does a good job of burning CO for those who want to burn the char.

Swirl is a method I use for getting more dwell time for the flame in the combustor section of the stove.  Swirl is not used for mixing because the gasses are thuroughly mixed by the Venturi gas mixer before they pass through the stationary fan.  Also swirl is not a good mixing method because it will seperate cooler denser gasses from hotter less dense gasses like a centrifuge.  I do not use turbulance for mixing because I believe the Venturi method is more thorough, though I agree with Dr. Larson that adding turbulance will improve combustion in a non-Venturi burner.  As with any mixing method, the Venturi method can be overwhelmed if to much wood gas is run through it, in agreement with Dean Still's statements.  So far my 6' diameter combustor can operate efficiently up to about 3 kw.  Above this both the mixer and stationary fan are not adiquate.  Adding more mixing capacity by adding more Venturi mixers helps with mixing, as three stove camp participants who helped me, Roberto, Steve and Cody showed me last week at Aprovecho's stove camp.  

The stationary fan has 6 blades and the shape of each blade is a smooth curve.  By the Coanda effect a flame up to 3kw can cling to the back side of the blade and leave the blade's trailing edge at a good flat angle.  A higher power flame produces so much buoyancy that the flame is seperated from the blade early and goes off at a fairly steep, not so good angle.  A new stationary fan design suggested by Dr. Larson may solve this problem and with additional Venturi mixers give the combustor the capability to handle higher power levels.  We shall see.

Best to all,

Kirk
  ----- Original Message ----- 
  From: Dean Still 
  To: Discussion of biomass cooking stoves 
  Sent: Tuesday, August 04, 2015 9:58 PM
  Subject: Re: [Stoves] Request to get partners in a possible TLUD stove improvement project


  Ron,


  IMO, swirl is not as powerful a cleaner stove technique compared to 1,) limiting the rate of woodgas being made or 2.) the generated mixing ability. We start by limiting the rate of reactions by decreasing primary air. Then add higher velocity jets of secondary air.


  Swirl is great but I think that it is gravy. May be wrong!


  Best,


  Dean


  On Tue, Aug 4, 2015 at 6:13 PM, Ronal W. Larson <rongretlarson at comcast.net> wrote:

    Dean:


    I want to emphasize - no making of a new stove intended.  This is to be only an addition to stoves that (hopefully, but not necessarily) have already been tested.  Looking for a breadth of existing designs.  Hopefully these are already in the best “balance” they could achieve.  This is to see whether that can be improved.


    What have you seen in swirl approaches?


    What have you seen in turbulence enhancers?


    Thanks for the quick feedback.


    Ron




    On Aug 4, 2015, at 6:52 PM, Dean Still <deankstill at gmail.com> wrote:


      Hi Ron,


      In my opinion, reducing emissions in a TLUD or any stove requires testing with emissions equipment. The great stove combines many factors working together. "Swirl" is only one part. Kirk gets good results when everything is in balance. "Swirl" is not powerful enough to overcome problems in the balance.


      I completely agree that anyone with tin snips and emission equipment and  perseverance can make low emission stoves. If you are lucky it takes a shorter time. So what? Even if you are unlucky it happens eventually. Drink more coffee.


      Best,


      Dean


      On Tue, Aug 4, 2015 at 5:40 PM, Ronal W. Larson <rongretlarson at comcast.net> wrote:

        Stove list  cc Kirk

                From what I can understand, the lowest emission (particulates, CO is easy) values from TLUDs have been from stoves designed and tested (last week) by Kirk Harris.  One reason seems to be that he has achieved a swirl, using (as described on this list often) a fan blade shape.

                I recall a few other uses of the term “swirl”, but know of no significant tests like those by Kirk.

                In recent conversations, Kirk has agreed to be part of an off-list TLUD stove group to investigate a different means of achieving swirl. It seems to be cheap and applicable to most TLUD stoves.

                The main advantage of a swirl is more flame time spent in the stove;  to get low emissions, hot gases, not flames, need to be hitting the cook pot.

                The proposed approach also should increase turbulence.  I do not recall any TLUD that tried to achieve turbulence  (to get the mixing needed for shorter path lengths and more complete combustion).  Anybody know of designs to achieve turbulence other than added disk or washer shapes?

                The reason for not saying much now is to save list members’ time and energy. This is not a guaranteed approach.

                 Anyone joining should want to see this open-source (no patents).

                Anticipated time commitment for a first design - a few hours with tin snips.  Metal cost a buck or two.  Probably can work with clay as well.

                If anyone knows of past swirl or turbulence experiments (or modeling) in TLUDs, your input now could save Kirk and I (and anyone else wanting to join) a lot of time - especially if those results were negative.

        Ron

                feel free to call 303-526-9629, if that would help.
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      -- 

      Dean Still
      Executive Director
      Aprovecho Research Center
      PO Box 1175
      76132 Blue Mountain School Road
      Cottage Grove, OR 97424
      (541) 767-0287
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  -- 

  Dean Still
  Executive Director
  Aprovecho Research Center
  PO Box 1175
  76132 Blue Mountain School Road
  Cottage Grove, OR 97424
  (541) 767-0287


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